1. The Field of the Invention
The present invention relates to card readers and in particular to a variable timing circuit which compensates for variations in speed of a card through the reader.
2. The Prior Art
The present invention is intended for use with a known card reader of the type manufactured by AMP Incorporated and identified as their magnetic card reader model 75. The read and write circuitry for this model card reader is disclosed in U.S. Pat. Ser. No. 692,411 now U.S. Pat. No. 4,053,936 filed June 3, 1976, the description of which is incorporated herein by reference.
The elements of this type of card reader are well known in the prior art and may be summarized as follows. A read head scans across an encoded portion of a magnetically coded card which is serially transported past the read head by a suitable transport mechanism. The read head includes an electromagnetic transducer which converts the magnetic coding into a useable signal which is supplied to a decoder circuit which is utilized to retrieve electronically stored information, to place in storage additional information, to provide a read out of information retrieved from storage.
Examples of known transport mechanisms for card readers can be found in U.S. Pat. Nos. 3,748,442; 3,836,753; and 3,896,293.
The card reader is designed to read plastic cards conforming with the fiscal magnetic and encoding format set forth by the American Banker's Association. Complete information concerning the cards is available in the American Banker's Association bank cards standards manual obtainable through 1120 Connecticut Avenue, N.W., Washington, D.C. 20036. The specifications generally can be summarized as being a plastic card 3.375 inches in width, 2.125 inches in height, 0.03 inches in thickness with a radius corner of 1.125 inches. The magnetic stripe on the card is a minimum of 0.25 inches in width and has a minimum length of 3.135 inches. The stripe of ferromagnetic material should be capable of producing 80 to 130% of the read head voltage output when written with a current 350 to 500% of a reference write head current. The reference is the NBS standard reference material 3200. The magnetic stripe is applied to the card at predetermined locations according to the system utilizing the card.
Even with the best of machines and the best of care, there can be many causes for variations of the speed of transport of a card through the reader. These variations have many causes, such as imperfect cards, worn transports, or voltage variations in those readers equipped with motors. Of course any variation in the speed of the card through the reader is a source of a potential erroneous reading of the information on the magnetic stripe.